The objective of this project is to define the initial, intra-cellular events of steroid hormone action. Synthetic glucocorticoid derivatives, some of which could potentially react to form covalent receptor-steroid complexes, are being used with glucocorticoid-responsive rat hepatoma tissue culture cells to examine: 1. steroid-receptor binding site interactions; 2. the effects of steroid binding on receptor conformation; 3. the nature of "activation" of receptor-steroid complexes and 4. the nuclear binding of activated receptor-steroid complexes. Fluorescence spectroscopy represents a novel technique for examining these interactions. For this reason, we have investigated the fluorogenic reaction of o-phtalaldehyde and beta-mercaptoethanol with primary amines and defined the fluorescent products as previously unknown, 1-alkylthio-2-alkylisoindoles. Further studies have been directed at adapting these isoindoles for a fluorescent study of steroid-receptor interactions. BIBLIOGRAPHIC REFERENCE: Simons, S.S., Jr. and Johnson, D.F.: The structure of the fluorescent adduct formed in the reaction of o-phthalaldehyde and thiols with amines. J. Amer. Chem. Soc. 98: 7098-7099, 1976.